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Homework Help: P-state lightwave

  1. Nov 22, 2004 #1
    Here's the question that i've tried working it out...but sorta blocked at some places:

    Write an expression for a P-state lightwave of angular frequency w and amplitude Eo propagating along a line in the xy-plane at 45° to the x-axis and having its plane of vibration corresponding to the xy-plane. At t=0, y=0, and x=0 the field is zero.

    And this is what i've done so far...so if anyone can help me out here or tell me if i'm going to the right direction that'll be great.

    i got: Eoy = Eo cos45°; Eox=Eo sin45° (in here, i'm not sure if i put the right axis or it's supposed to be Eoy and Eoz)
    E(x,t) = Eo cos(kx-wt+1/4π) (once again, i dunno if it's E(x,t) and i assumed that there's no component for the j and k vector)???

    kinda lost :blushing:
  2. jcsd
  3. Nov 22, 2004 #2
    i think the wave should be propagating in the z direction if it's propagating at 45 degrees to the x-axis, it's also at 45 degrees to the y-axis.

    So, i think you're looking for something more like

    E(z,t)=Eo Cos(kz-wt) or something..

    i've got an exam in the subject in a weeks time and i'm a little lost too :-)
  4. Nov 22, 2004 #3


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    The wavenumber is a vector related to the wavelength and corresponds to the direction of propagation so in your case

    [tex]\vec k = \frac {2\pi}{\lambda} \frac {\hat i + \hat j}{\sqrt 2} = \frac {\omega}{c} \frac {\hat i + \hat j}{\sqrt 2}[/tex]

    where the latter expression holds only in vacuum so your wave will have components containing sines and cosines of the phase [itex]\vec k \cdot \vec x - \omega t[/itex].
  5. Oct 27, 2011 #4
    How do you get the sqrt(2)? (nvmd its probably from the new unit vector)
    Last edited: Oct 27, 2011
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